1. Field of the Invention
The present invention relates to protective wildlife guards for electrical power distribution equipment.
2. Description of the Related Art
Distribution equipment used to supply electrical power has used wildlife protection guards or covers to prevent wildlife from simultaneously contacting energized and grounded surfaces. If such contact occurred, short circuits and consequent power outages frequently were the result. Service interruptions are undesirable to both customers and the electrical utility. Even momentary service interruptions are a nuisance for customers because they have required customers to reset digital clocks and other such devices. For utilities, service interruptions have required field service personnel to replace blown fuses and to repair or replace damaged equipment. For example, a circuit breaker in a substation and thus for an entire circuit might operate and hundreds of customers could have service interrupted as a result of a single wildlife-caused short circuit. Manufacturing facilities with sensitive processes often cannot tolerate even momentary power interruptions. For these reasons, wildlife protection guards or covers were developed to protect vulnerable energized parts of distribution equipment.
There have generally been two types of wildlife guards. One such type of guard is a generally disk- or plate-shaped barrier. Commonly owned U.S. Pat. No. 5,864,096 issued Jan. 26, 1999, is an example of the disk or plate type wildlife guard. The other type of guard is of a hinged cover or enclosure type which was fitted over a portion of the equipment and secured there. There have been several commercially available products of the enclosure type. However, there have been several problems with these types of enclosures.
Sparkgap bars or probes are sometimes provided near the bushing terminal connection of the electrical conductors to the distribution equipment, such as transformers. They are normally used in areas with heavy environmental contamination, such as coastal areas which have salt contamination. The sparkgap bars serve to provide external air gaps between the equipment bushing and the surge arrester. Without the air gaps, leakage currents on the contaminated surfaces of the arresters will cause spurious sparkovers of many arresters and this can cause many arresters to fail prematurely. The air gaps provided by the sparkgap bars serve to isolate the arrester from the energized phase conductors, but only during normal operating voltage conditions. When lightning surge voltages occur, the sparkgap bars sparkover in order to shunt lightning surge current away from the protected equipment and through the surge arrester thus protecting the equipment.
When wildlife guards were installed, the cover would serve as an insulative barrier, preventing a sparkover of a sparkgap unless access through them was provided. Certain wildlife guards provided weakened areas at certain specific locations in the walls of the covers. Line crew members could then cut, punch out or otherwise remove a portion of the cover wall at one of these locations during installation. The resultant hole or gap in the cover allowed sparkgap bar passage through the wall if the location of the sparkgap bar coincided with one of the pre-designed locations.
Unfortunately, field conditions vary widely and the sparkgap bar locations with respect to the electrical equipment bushing geometry could often vary widely. There was no way, so far as is known, to know in advance the area where a portion of the wall of the wildlife cover would need to be removed in order to permit sparkgap bar access through the wall of the cover. Line crews might often attempt to improvise and use some makeshift solution, such as bending the sparkgap bar or force-fitting the cover in place. Unfortunately, bending the sparkgap bar increases the air gap distance which increases the sparkover voltage which can cause failure of the protected equipment. Also, the covers might later work loose and leave the electrical connection exposed. If the temporary makeshift measures became ineffective, the wildlife protective function for which the covers were intended was thus defeated.
At times during usage, it also may have been necessary to remove the wildlife protective cover once installed. Examples would include removal in order to have access to the electrical equipment in order to disconnect the equipment. The housings of the covers were required to be firmly closed by some mechanical locking mechanism when installed. This was done in order to prevent their coming inadvertently loose and failing in their protective function. Unfortunately, the lock mechanisms of previous cover designs keep lock mechanism parts under mechanical stress. This frequently has caused the lock mechanisms to break over time, especially in cold weather conditions where the cover material normally becomes more brittle. When the lock mechanisms break, the covers open and their protective purpose is defeated.
A number of the presently available cover type housings were difficult to remove. The covers did not have lock release mechanisms and were difficult to grasp once installed because the bottom opening of the cover was often inaccessible between insulator skirts. For this reason, large amounts of effort were often required to open the locking mechanism. Line crew members would often be required to grasp the cover with both hands and compress or otherwise distort the shape of the cover in order to force the latch mechanisms open. In addition, if at times too much force was exerted, cover locking mechanism would be broken on opening it. This rendered the wildlife cover unsuitable for further use.
In other installation conditions, the conductor would be arranged on the equipment so that it extended horizontally both to and away from the connection to the equipment. Since the protective cover wildlife guards were typically hinged, this presented a problem. The conductors could not be installed through the pivotable sidewalls of the cover, since the sidewalls needed to move in order to close the cover in place when installed. The hinge areas of the pivotable covers typically were of considerable height along the cover walls. The hinges thus made installation of covers difficult in these situations. Again, the line crew would be forced to use makeshift measures or improvisations.
Protective enclosure type wildlife guards were normally mounted on insulative skirts of transformer bushings to protect the electrical connection of the power conductor to the transformer. For a given electric utility or power company, there were a wide variety of inner diameter or cores and outer skirt diameters for bushings on the different types of power distribution equipment in use. Thus, to accommodate the range of outer skirt diameters, a range of sizes of covers was required to be carried on line crew or service trucks, where storage space at a premium. Unfortunately, this failed to accommodate the range of inner diameter or cores. Later, there were attempts to make bottom closure walls flexible in these enclosure covers to accommodate the range of core and skirt diameters. This may have reduced the number of sizes of covers required by some utilities. However, the strength and structural integrity of the cover suffered in the areas where flexibility was offered to accommodate some bushing sizes where the inner diameter or core was only slightly less than the outer skirt diameter. In these cases, the flexible portions were too large and would permit the cover to come loose from its insulative bushing and again defeat the wildlife protective purpose of the cover. Furthermore, the inner opening of the flexible bottom closure wall was frequently too small for the bushing core diameter to allow closure of the cover around the bushing.